The overall goal of my research is to understand quorum sensing: the process of cell-cell communication in bacteria. The proposed research will probe how quorum sensing functions in relatively natural environments that contain multiple species of bacteria, are spatially and temporally heterogeneous, and undergo fluctuations in conditions. At the most general level, the proposed work will provide insight into intra- and inter species communication, population-level cooperation, and the network principles underlying signal transduction and information processing. At a more specific level, the research will advance the understanding of the specific chemical inputs and genetic outputs of quorum sensing, the mechanisms underlying small-RNA-mediated control of gene expression, and the evolutionary and physico-chemical drivers of biofilm formation. At a practical level, my group's investigations could lead to strategies for controlling quorum sensing, including development of anti-microbial drugs aimed at bacteria that use quorum sensing to control virulence and biofilm formation, and improved industrial production of natural products. The proposed research relies on in vivo genetic manipulation and phenotypic analyses of Vibrio cholerae and Vibrio harveyi. The research employs in vitro biochemical assays with purified proteins, DNA, and small molecule ligands, whole-genome microarrays, ChIP-sequencing, and fluorescent imaging. We will also use fluorescence microscopy combined with microfluidics to quantify quorum sensing in individual bacterial cells in liquid cultures and in biofilm chambers of different geometries and under different flow and perturbation conditions.